Graves' disease (GD) is a condition where the thyroid is overactive, producing too many hormones. This study is checking if a new medicine called IMVT-1402 is safe and works well for adults with GD who still have high thyroid levels even after taking other drugs, called antithyroid drugs (ATD). The study is randomized, which means participants will be randomly chosen to receive either the medicine or a placebo, a pill that doesn’t have any medicine in it. It’s also double-blind, so neither the participants nor the researchers will know who is getting the medicine or the placebo. To join, participants must be 18 or older, have GD, and have tried ATD treatment without success.

• The study is global and will take place at multiple centers.
• Participants should not have had certain treatments like radioactive iodine (RAI) or thyroid surgery.
• This study phase is called Phase 2b, focusing on the effectiveness and safety of the treatment.